The invention pertains to a spike for motor vehicle tires, especially for snow tires of automobiles. In order to make it possible for the spike to accept the maximal force from below, e.g., a frozen or snowy street, German Utility Model No. 1,850,309 teaches that the spikes in top view (i.e., in the radial view from the outside to the inside) should be out-of-round, i.e., flat or flat-oval.
Each spike contains a plate-like root, which serves to anchor the spike in the tire in the vicinity of the upper radial ply. The part of the spike that does not form the root is hereinafter called the upper part of the spike. At least a part of the upper part of the spike protrudes out of the running surface of the tire. The root of the spike can be just as out of round as the upper part of the spike. The upper part of the spike can have a thicker spike part, to which a tapered, pointed part is joined radially outward, which protrudes out of the rubber running surface.
An objective of the invention is to improve a spike of the generic type in such a way that a tire equipped therewith is able to accept even larger forces from below. Another objective of the invention is to create a comparably improved tire and a third objective is to produce such a tire.
The above and other objectives of the invention can be achieved with a spike for the running surface of a motor vehicle tire, especially a snow tire with an out-of-round, longitudinal, plate-like spike root, whose greatest extension defines a longitudinal axis, and with an out-of-round, longitudinal spike upper part, whose greatest extension defines a longitudinal axis, characterized in that the spike root and the spike upper part are twisted in relation to each other, so that the longitudinal axis of the spike root together with the longitudinal axis of the spike upper part encloses an angle varying from zero.
Preferably, the angle enclosed by the two longitudinal axes is between 65xc2x0 and approximately 115xc2x0, and more preferably essentially 90xc2x0. In addition, preferably a longitudinal extension of the thicker part is essentially the same as a width extension of the root. It is also preferred that the upper part consists of a thicker spike part and a tip sitting thereon, and the tip has an out-of-round cross section, while a longitudinal axis of the tip is oriented essentially parallel to the longitudinal axis of the thicker part.
In another aspect of the present invention, there is provided a snow tire for motor vehicles with a running surface having a plurality of protruding spikes, each with an upper part, protruding at least in part from the running surface and anchored in the tire by means of a root, which are distributed over the width and the circumference of the running surface.
Preferably the spikes are arranged in the middle (M) of the running surface, the longitudinal axes of the roots are essentially oriented in the circumferential direction of the tire and the longitudinal axes of the upper parts are essentially axial. In addition, it is preferred that the edge areas (S) of the running surface of the tire, spikes are arranged, in which the longitudinal axes of the root and the spike upper part enclose an angle that varies from 90xc2x0. It is also preferred that the spikes anchored in the running surface have several different configurations of the roots.
Furthermore, yet another aspect of the invention provides a process for producing a snow tire with a running surface, as described above, and with spikes, as described above, in which the spikes, after completion of the formation of the blank running surface, are shot, preferably while the running surface is still unvulcanized, into the running surface, wherein the injection pipes, in which the spikes are accelerated prior to the impact on the periphery of the running surface, have such a clear cross section that this cross section surrounds the top view of each of the spikes to be mounted with slight play, in order to guide the spike securely free of torsion and seat it in the proper angular position.
With the design of the root plate and the upper part of the spike, each with oblong outline and the approximately right-angled (65-115xc2x0) orientation of both longitudinal axes, the buckling of the spike can be greatly reduced, which improves the ability to accept force from below. Surprisingly, the higher burden of the thusly oriented spike root itself and its contact with the surrounding rubber, especially the upper radial ply, has been shown to be unproblematical.
The longitudinal axis of the plate-like root of a spike according to the inventions, encloses with the longitudinal axis of the upper part, an angle greater than zero, preferably 65-115xc2x0, ideally 90xc2x0.
The upper part of the spike is conveniently configured in the middle of the running surface such that the longitudinal axis of the approximately oval or ellipsoidal top view of the spike approximates an axial line. In this manner, this running surface area can transfer the greatest forces in the circumferential direction, which shortens the braking distance and improves traction (thrust).
For most snow tires, it is nevertheless more important to be able to transfer sufficient lateral force on ice as well, so as to ensure directional stability and curve tracking. Such forces can be best transferred by the sidewalls of the tires, the surface pressure of which intensifies on the outer side of the curve when driving in a curve. For this reason, the upper parts of the spikes are expediently installed in the sidewalls of the tires rotated at least so far with respect to the axial that the top view of the longitudinal axis describes an angle of at least 30xc2x0 to the axial. For an automobile snow tire, an angle of 45xc2x0 appears to be especially favorable; for a truck snow tire, even more, e.g., 60xc2x0, since the latter, due to the great wheel diameter and therefore the long contact surface, already has a good longitudinal force transfer capacity. In the case of a motorcycle tire, it is practical for the sidewall spikes to be arranged such that the top view longitudinal axis is exactly oriented in the circumferential direction so as to maximize the transfer capacity of the transverse forces. In the case of tires for trailers without brakes, the latter holds true for all spike positions.
For all spikes whose upper part is axially oriented, i.e., the longitudinal axis of the longitudinal top view of the spikes runs along an axial, as discussed in the penultimate paragraph, the optimal twisting angle between the upper part and the root is also 90xc2x0. The root is then oriented circumferentially in the finished tire and imparts to the spike the smallest possible deformation under forces in the circumferential direction.
For all spikes whose upper part is circumferentially oriented, i.e., the longitudinal axis of the longitudinal top view of the spikes runs in the circumferential direction, as discussed at the end of the penultimate paragraph, the optimal twisting angle between the upper part and the root is likewise 90xc2x0. In the finished tire, the root is then oriented axially and imparts to the spike the smallest possible deformation under forces in the axial direction.
For all spikes whose upper part is oriented diagonally, i.e., the longitudinal axis of the elongated spike top view runs at an angle greater than 0xc2x0 and less than 90xc2x0 to the circumferential, as discussed at the beginning of the penultimate paragraph, the optimal twisting angle between the upper part and the root is 90xc2x0 only if the latter run precisely on the equator (zenith) of the tire, which is not preferred, however. In the finished tire, the root is then complementarily oriented diagonally to the circumferential direction, so that, e.g., when in a first rotational sense the upper part rotates some 30xc2x0 to the circumferential direction, the root is oriented by 60xc2x0 (or between about 90xc2x0 to about 30xc2x0) in the inverse rotational sense to the circumferential direction.
For all spikes whose upper part is diagonally oriented and which lie outside the equator of the tire, the preferred location, the optimal twisting angle varies from 90xc2x0, all the more so, the more ball-like the running surface of the tire and the packet of radial plies are, the closer the spike is to the edge of the running surface, and the more the angle in which the top-view longitudinal axis of the upper part of the spike varies from the nearest xe2x80x9cpurexe2x80x9d angle, 0xc2x0 or 90xc2x0. The findings calculated heretofore are interpreted as indicating that the longitudinal axis alignment for the spike root should encompass, with the circumferential direction, an angle more acute by a value X than would be represented by a 90xc2x0 twist between the upper part and the root. This value X can be determined by the typical person skilled in the art by way of an FEM optimization (FEM=Finite Elements Method for calculating mechanical stresses and deformations); it can be as great as half the inclination angle to the circumferential direction.
In addition to better frictional contact with the surface below during operation, tires equipped with the spikes according to the invention provide the advantage that the flexing work of the spikes in the rubber of the running surface of the tire is reduced, since, due to the lengthening of the plate-like root of the spike and therefore the lever arm for receiving the pitching moment, all of the deformation ways are reduced. This reduces the heating of the running surface during operation and thus delays the aging of the rubber, which in turn explains why the tread separation tendency between the root of the spike and the lower rubber layer which is associated with the stiffer anchoring of the spikes leads to no damage even in continuous operation.
The invention is explained in greater detail below with references to the appended drawings of several embodiments.